Electrochemical oscillations and bistability during anodic dissolution of vanadium electrode in acidic media—part II. The model

摘要

Following our experimental results on the oscillatory and bistable vanadium electrooxidation in phosphoric acid medium (Gorzkowski et al., 2011), we constructed a theoretical model of the V/H₃PO₄ passivation/dissolution system which allowed us to reproduce the basic dynamic instabilities observed. In this model, the formation of the negative resistance (N-NDR) region was ascribed to the potential-dependent formation/destruction of the inhibitive V₂O₅ layer on the electrode surface. The dynamic system was defined in terms of two variables: electrode potential and surface concentration of VO₂+ species. Both relaxation oscillations and bistability for conditions similar to the experimental ones were obtained in numerical calculations and a theoretical bifurcation diagram was constructed. The analysis of the system’s dynamics in terms of nullclines allowed us to detect directly unattainable unstable steady states associated with both the oscillatory and bistable regimes.